Molten Salt Bath, Deposit Obtained Using The Molten Salt Bath, Method Of Manufacturing Metal Product, And Metal Product

ABSTRACT

A molten salt bath includes at least one kind selected from the group consisting of chlorine, bromine, and iodine, zinc, at least two kinds of alkali metals; and fluorine. Here, the molten salt bath may include oxygen. Furthermore, the molten salt bath may include at least one kind selected from the group consisting of tungsten, chromium, molybdenum, tantalum, titanium, zirconium, vanadium, hafnium, and niobium. Additionally provided are a deposit obtained using the aforementioned molten salt bath, a method of manufacturing a metal product using the aforementioned molten salt bath, and a metal product.

TECHNICAL FIELD

The present invention relates to a molten salt bath, a deposit obtained using this molten salt bath, a method of manufacturing a metal product, and a metal product.

BACKGROUND ART

Conventionally, when a metal product is manufactured by electroforming or a substrate is coated, a technique of depositing a metal in a bath by electrolysis is used. Specifically, in recent years, in various fields of information communication, medical care, biotechnology, automobiles and the like, MEMS (Micro Electro Mechanical Systems) receive attention which allows production of fine metal products that are compact in size, have high performance and are energy-efficient. It is contemplated to manufacture a fine metal product applicable to MEMS or to coat the surface of the fine metal product using the technique of deposing a metal by electrolysis.

On the other hand, since metals (refractory metals) such as tungsten and molybdenum of the fourth to sixth period of Group IVA-Group VIA of the periodic table are heat-resistant and corrosion-resistant, these metals can be used for the above-noted fine metal product to manufacture a fine metal product with high heat-resistance and durability.

Non-Patent Document 1: P. M. COPHAM, D. J. FRAY, “Selecting an optimum electrolyte for zinc chloride electrolysis”, JOURNAL OF APPLIED ELECTROCHEMISTRY 21 (1991), p. 158-165

Non-Patent Document 2: M. Masuda, H. Takenishi, and A. Katagiri, “Electrodeposition of Tungsten and Related Voltammetric Study in a Basic ZnCl₂—NaCl (40-60 mol %) Melt”, Journal of the Electrochemical Society, 148(1), 2001, p. C59-C64

Non-Patent Document 3: Akira Katagiri, “Electrodeposition of Tungsten in ZnCl₂—NaCl and ZnBr₂—NaBr Melts”, Molten Salts and High-temperature Chemistry, Vol. 37, No. 1, 1994, p. 23-38

Non-Patent Document 4: Nikonowa I. N., Pawlenko S. P., Bergman A. G., “Polytherm of the Ternary System NaCl—KCl—ZnCl₂”, Bull. acad. sci. U.R.S.S., Classe sci. chim. (1941), p. 391-400

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, although metals such as nickel and copper can be deposited by electrolysis after being dissolved in water, refractory metals cannot be deposited by electrolysis using aqueous solution.

Then, for example, a molten salt bath formed by melting, for example, a zinc chloride or bromide, a sodium chloride or bromide, and a refractory metal compound is used to deposit a refractory metal by electrolysis. However, the purity, density and denseness of the resulting deposit is low, and in addition, the surface of the deposit is coarse.

An object of the present invention is to provide a molten salt bath allowing production of a refractory metal deposit with high purity, high density and high denseness and having a smooth surface, a deposit obtained using the molten salt bath, a method of manufacturing a metal product, and a metal product.

Means for Solving the Problems

The present invention provides a molten salt bath including at least one kind selected from the group consisting of chlorine, bromine and iodine, zinc, at least two kinds of alkali metals, and fluorine.

Here, the molten salt bath of the present invention may include oxygen.

The molten salt bath of the present invention may include at least one kind selected from the group consisting of tungsten, chromium, molybdenum, tantalum, titanium, zirconium, vanadium, hafnium, and niobium.

The molten salt bath of the present invention may be made of at least two kinds selected from the group consisting of sodium, potassium and cesium as the alkali metals, at least one kind of chlorine and bromine, zinc, and fluorine.

Preferably, in the molten salt bath of the present invention, a zinc content is at least 14 atomic % and at most 30 atomic % of the molten salt bath as a whole.

Preferably, in the molten salt bath of the present invention, a zinc content is at least 17 atomic % and at most 25 atomic % of the molten salt bath as a whole.

Preferably, in the molten salt bath of the present invention, a fluorine content is at least 0.1 atomic % and at most 20 atomic % of the molten salt bath as a whole.

The present invention also provides a deposit obtained using any of the above-noted molten salt bath. Here, the deposit of the present invention is preferably formed in a state in which the molten salt bath includes at least 0.01 atomic % of oxygen.

Preferably, arithmetic mean roughness Ra (JIS B0601-1994) of a surface of the deposit of the present invention is at most 3 μm.

Preferably, a relative density of the deposit of the present invention is at least 85%.

The present invention additionally provides a method of manufacturing a metal product including the steps of: forming a resist pattern on a conductive substrate to expose a part of the conductive substrate; immersing the conductive substrate having the resist pattern formed thereon in any of the above-noted molten salt bath; and depositing a metal from the molten salt bath on the exposed part of the conductive substrate. Here, in the method of manufacturing a metal product, the temperature of the molten salt bath may be at most 250° C.

The present invention further provides a metal product manufactured using the method of manufacturing a metal product as described above.

EFFECTS OF THE INVENTION

In accordance with the present invention, it is possible to provide a molten salt bath allowing production of a refractory metal deposit with high purity, high density and high denseness and having a smooth surface, a deposit obtained using the molten salt bath, a method of manufacturing a metal product, and a metal product.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic configuration view illustrating an exemplary method of obtaining a deposit using a molten salt bath in accordance with the present invention.

DESCRIPTION OF THE REFERENCE SIGNS

1 electrolytic tank, 2 molten salt bath, 3 anode, 4 cathode

BEST MODES FOR CARRYING OUT THE INVENTION

The present invention provides a molten metal salt bath including at least one kind selected from the group consisting of chlorine, bromine and iodine, zinc, at least two kinds of alkali metals, and fluorine. Here, at least two kinds of lithium, sodium, potassium and cesium are included as alkali metals in the molten salt bath of the present invention. The form in the molten salt bath of at least one kind selected from the group consisting of chlorine, bromine and iodine, zinc, at least two kinds of alkali metals, fluorine, and the like that constitute the molten salt bath of the present invention is not specifically limited. For example, these components may be present as ions or may be present in a state of forming a complex in the molten salt bath. The above-noted components that constitute the molten salt bath of the present invention can be detected by conducting ICP (Inductively Coupled Plasma) spectrometry for a sample prepared by dissolving the molten salt bath of the present invention in water.

In addition to the above-noted constituent components, the molten salt bath of the present invention may include oxygen. If the molten salt bath of the present invention includes oxygen, a deposit with higher purity, higher density and higher denseness and having a smoother surface may be obtained. The form of oxygen in the molten salt bath of the present invention is also not specifically limited and, for example, oxygen may be present as ions or may be present-in a state of forming a complex or in the state of oxide.

It is noted that the presence of oxygen in the molten salt bath of the present invention may be identified by using an inert gas fusion infrared absorption method for the molten salt bath of the present invention. Here, the inert gas fusion infrared absorption method is performed, for example, as follows. First, the molten salt bath is put into a carbon crucible in a helium gas atmosphere and the carbon crucible is heated to cause production of oxygen from the molten salt bath. Then, this oxygen reacts with carbon of the carbon crucible to produce carbon monoxide or carbon dioxide. Then, infrared radiation is applied in the atmosphere including the produced carbon monoxide or carbon dioxide. Finally, the amount of attenuation of infrared radiation which is caused by absorption by carbon monoxide or carbon dioxide in the atmosphere is examined to identify the presence and content of oxygen in the molten salt bath.

At least one kind selected from the group consisting of tungsten, chromium, molybdenum, tantalum, titanium, zirconium, vanadium,, hafnium, and niobium may be included in the molten salt bath of the present invention. These metals are refractory metals in the fourth to sixth periods of Group IVA-Group VIA of the periodic table. When electrolysis is performed using the molten salt bath of the present invention including these refractory metals, it is possible to obtain a deposit including these metals as a main component with high purity, high density and high denseness and having a smooth surface. The form of tungsten, chromium, molybdenum, tantalum, titanium, zirconium, vanadium, hafnium, or niobium in the molten salt bath of the present invention is not specifically limited and, for example, they may be present as ions or may be present in a state of forming a complex.

The refractory metal content in the molten salt bath is preferably 0.04 atomic % where the entire components that constitute the molten salt bath is 100 atomic %, in view of obtaining a refractory metal deposit with high purity, high density and high denseness and having a smooth surface. The refractory metal deposit can be obtained more efficiently with a higher refractory metal content in the molten salt bath since deposition with high current density is possible. However, when the refractory metal content is increased, the melting point of the molten salt bath rises and the temperature of the molten salt bath in electrolysis needs to be increased. Therefore, if the refractory metal content is increased, it may become impossible to conduct electrolysis by immersing a conductive substrate having a resist pattern made of a material having a low melting point such as a resin in the molten salt bath. Thus, the refractory metal content is preferably set as appropriate depending on a purpose.

The presence and content of the refractory metal in the molten salt bath of the present invention can be detected and calculated by conducting ICP spectrometry for a sample prepared by dissolving the molten salt bath of the present invention in water. It is noted that although the present invention aims to obtain a refractory metal deposit with high purity, high density and high denseness and having a smooth surface, it is needless to say that a deposit other than a refractory metal may be obtained using the molten salt bath of the present invention.

Preferably, the molten salt bath of the present invention is made of at least two kinds selected from the group consisting of sodium, potassium, and cesium as the aforementioned alkali metals, at least one kind of chorine and bromine, zinc, and fluorine. In this case, it is likely that a deposit with higher purity, higher density and higher denseness and having a smoother surface can be obtained. Here, desirably, a component other than at least two kinds selected from the group consisting of sodium, potassium, and cesium, at least one kind of chorine and bromine, zinc, and fluorine is not present in the molten salt bath except for an inevitably included component.

The zinc content in the molten salt bath of the present invention is preferably 14 atomic % or more and 30 atomic % or less, more preferably, 17 atomic % or more and 25 atomic % or less, in the entire molten salt bath. If the zinc content is less than 14 atomic % or more than 30 atomic % of the entire molten salt bath, a deposit with high purity and high density and having a smooth surface is not likely to be obtained. On the other hand, if the zinc content is 17 atomic % or more and 25 atomic % or less of the entire molten salt bath, the temperature of the molten salt bath can be set at 250° C. or lower. Therefore, even when an electroforming mold having a resist pattern of a resin such as polymethyl methacrylate (PMMA) formed on a conductive substrate is immersed, deformation of the resist pattern due to the temperature of the molten salt bath can be prevented. Thus, in this case, it is possible to manufacture a metal product by electroforming at a low temperature of 250° C. or lower as the temperature of the molten salt bath. It is noted that the zinc content in the molten salt bath of the present invention can be detected by conducting ICP spectrometry for a sample prepared by dissolving the molten salt bath of the present invention in water.

Here, for example, a substrate made of a metal alone or an alloy, a substrate formed by plating a non-conductive substrate such as glass with a conductive metal, or the like can be used as a conductive substrate. A metal product is formed by depositing a metal such as refractory metal in the molten salt bath by electrolysis on that part of the surface of the above-noted conductive substrate which is exposed without formation of a resist pattern. The metal product manufactured in accordance with the present invention includes, for example, contact probes, micro-connectors, micro-relays, a variety of sensor parts, or the like. The metal product manufactured in accordance with the present invention includes, for example, RFMEMS (Radio Frequency Micro Electro Mechanical System) such as variable capacitors, inductors, arrays, or antennas, optical MEM members, ink jet heads, electrodes in biosensors or power MEMS members (electrodes or the like).

If the fluorine content in the molten salt bath of the present invention is too low, the effect of inclusion of fluorine cannot be achieved, and if too high, the likeliness of incorporation of fluorine into the deposit as an impurity is increased. Therefore, the fluorine content in the entire molten salt bath is preferably 0.1 atomic % or more and 20 atomic % or less, and more preferably 0.1 atomic % or more and 4 atomic % or less. It is noted that the fluorine content in the molten salt bath of the present invention can be detected and calculated using a fluoride ion-selective electrode for a sample prepared by dissolving the molten salt bath of the present invention in water.

The molten salt bath of the present invention can be obtained by mixing at least a zinc chloride, bromide or iodide, at least two kinds of alkali metal chloride, bromide or iodide, and a fluorine compound, followed by heating for melting.

The resulting molten salt bath is put into an electrolytic tank 1, for example, shown in the schematic configuration view in FIG. 1. Then, after an anode 3 and a cathode 4 are immersed in molten salt bath 2 put in electrolytic tank 1, electrolysis of molten salt bath 2 is performed by feeding electric current between anode 3 and cathode 4, whereby the metal included in molten salt bath 2 is deposited, for example, on the surface of cathode 4, resulting in a deposit.

Here, the deposit is preferably formed in the state in which 0.01 atomic % or more of oxygen is contained in molten salt bath 2. In this case, it is likely that a purer deposit can be obtained. The technique to include oxygen into molten salt bath 2 may include, for example, performing the processes from preparation of molten salt bath 2 to obtaining a deposit, in the air, introducing oxygen in molten salt bath 2, preparing molten salt bath 2 mixed with an oxide, or the like. It is noted that the above-noted oxygen content is represented in a ratio (atomic %) where the total of the entire components that constitute molten salt bath 2 including oxygen is 100 atomic %. The oxygen content in molten salt bath 2 can be calculated using the aforementioned inert gas fusion infrared absorption method.

Preferably, the surface of the deposit has surface roughness of 3 μm or less in view of obtaining a deposit having a smooth surface. Here, in the present invention, “surface roughness” refers to arithmetic mean roughness Ra (JIS B0601-1994).

Preferably, the relative density of the deposit is 85% or more. If the relative density of the deposit is less than 85%, voids in the deposit are increased so that salts are more likely to be caught. In addition, the residual stress in the deposit increases so that the deposit may be stripped during formation of the deposit. Here, in the present invention, “relative density of the deposit” is a ratio (%) of the density (g/cm³) of the deposit to the original density (g/cm³) of the metal intended to be formed, as expressed by the following formula:

the relative density of the deposit (%)=100×(the density of the deposit)/(the original density of the metal intended to be deposited).

EXAMPLE Example 1

ZnCl₂ (zinc chloride), NaCl (sodium chloride), KCl (potassium chloride), and KF (potassium fluoride) powders were each dried in a vacuum oven at 200° C. for 12 hours. WCl₄ (tungsten tetrachloride) powder was dried in a vacuum oven at 100° C. for 12 hours. Then, after ZnCl₂, NaCl and KCl powders were each weighed in a glove box under Ar (argon) atmosphere in a mol ratio of 60:20:20, these powders were put into an alumina crucible in the same glove box.

In addition, after KF and WCl₄ powders were each weighed in the above-noted glove box such that there were 4 mol of KF and 0.54 mol of WCl₄ for 100 mol of the ZnCl₂, NaCl and KCl mixture put in the alumina crucible, these powders were put into the above-noted alumina crucible. The composition (mol ratio) of the raw materials put in the alumina crucible is shown in Table 1.

Then, the alumina crucible that contained ZnCl₂, NaCl, KCl, KF, and WCl₄ was heated in the above-noted glove box to allow the powders in the alumina crucible to be melted. Thus, 500 g of the molten salt bath of Example 1 was prepared. The composition (atomic %) of this molten salt bath is shown in Table 2. It is noted that the composition of the molten salt bath shown in Table 2 is calculated based on the composition of ZnCl₂, NaCl, KCl, KF, and WCl₄ contained in the above-noted alumina crucible.

Then, a mirror-polished nickel plate having arithmetic mean roughness Ra (JIS B0601-1994) of less than 10 nm as a cathode and a tungsten rod having a diameter of 5 mm as an anode were immersed in the molten salt bath of Example 1 in the above-noted glove box. Subsequently, with the temperature of the molten salt bath kept at 250° C., electric current is fed across the aforementioned electrodes for 10 hours such that current of 3 mA per cm² of the nickel plate (current density 3 mA/cm²) flows. Electrolysis performed under such electrolytic conditions (Table 3) resulted in a deposit including tungsten on the surface of the nickel plate serving as a cathode.

Thereafter, the nickel plate having the deposit including tungsten was taken out from the glove box into the air, and the deposition state, composition, surface roughness and density of the deposit were each evaluated. The result is shown in Table 3.

It is noted that the deposition state of the deposit was evaluated by determining. whether or not the deposition was in a state of a film that is firmly attached to the nickel plate, through the observation using SEM (Scanning Electron Microscope). In this observation, if the film state was achieved, the electrodeposition was evaluated as good, and if the deposit was formed in a grain state or the deposit was cracked, the electrodeposition was evaluated as no good.

In addition, the composition of the deposit was evaluated by ICP spectrometry after the deposit was dissolved in acid. As the amount of tungsten contained in the deposit was larger (with the larger atomic % of tungsten (W) shown in Table 3), it was evaluated that a higher purity was achieved. The components other than W, Zn and O shown in Table 3 (the other fields in Table 3) were mainly the constituent components of the molten salt bath and were present in the cavities of the deposit. Therefore, as the amount of the components other than W, Zn and O was smaller (with the smaller atomic % in the other fields of Table 3), the deposit was evaluated as having higher denseness.

Furthermore, the surface roughness of the deposit was evaluated using a laser microscope (manufactured by KEYENCE CORPORATION, model No. “VK-8500”). It is shown that as the numeric value of the surface roughness shown in Table 3 is smaller, the deposit has a smoother surface. It is noted that the surface roughness shown in Table 3 is arithmetic mean roughness Ra (JIS B0601-1994).

The density of the deposit was evaluated using an FIB (Focused Ion Beam) apparatus by cutting out the vicinity of the center of the deposit in a rectangular shape of 3 mm×3 mm together with the nickel plate and thereafter calculating the density of the deposit in the cut sample. It is noted that the density of the deposit was calculated as follows. First, using the FIB apparatus, the thickness of the deposit in the sample was measured. Then, the volume of the deposit was calculated by multiplying the measured thickness by the area (3 mm×3 mm) of the surface of the deposit. On the other hand, the mass of the part corresponding to the cut nickel plate was calculated based on the mass of the entire nickel plate that was measured beforehand. Then, the mass of the entire sample was measured, and the mass of the deposit was calculated by subtracting the mass of the part corresponding to the cut nickel plate as described above from the measured mass of the entire sample. Finally, the density of the deposit was calculated by dividing the mass of the deposit by the volume of the deposit.

Furthermore, the relative density of the deposit (%) was calculated by the. following formula based on the density of the deposit calculated above and the original density of tungsten, where the original density of tungsten which is a metal intended to be deposited is 19.3 (g/cm³):

the relative density (%) of the deposit=100×(the density of the deposit)/(the original density of tungsten).

As shown in Table 3, the deposit obtained by using the molten salt bath of Example 1 was in the film-like deposition state, and had a large amount of tungsten with high purity, and with a small surface roughness, high density, high relative density and high denseness.

Example 2

ZnCl₂, NaCl, KCl, LiCl (lithium chloride), and KF powders were each dried in a vacuum oven at 200° C. for 12 hours. WCl₄ powder was dried in a vacuum oven at 100° C. for 12 hours. Then, after ZnCl₂, NaCl, KCl, and LiCl powders were each weighed in a glove box under Ar atmosphere in a mol ratio of 35:30:30:5, these powders were put into an alumina crucible in the same glove box.

In addition, after the KF and WCl₄ powders were each weighed in the above-noted glove box such that there were 4 mol of KF and 0.54 mol of WCl₄ for 100 mol of the ZnCl₂, NaCl, KCl, and LiCl mixture put in the alumina crucible, these powders were put into the above-noted alumina crucible. The composition (mol ratio) of the raw materials put in the alumina crucible is shown in Table 1.

Then, the alumina crucible that contained ZnCl₂, NaCl, KCl, LiCl, KF, and WCl₄ was heated in the above-noted glove box to allow the powders in the alumina crucible to be melted. Thus, 500 g of the molten salt bath of Example 2 was prepared. The composition (atomic %) of this molten salt bath is shown in Table 2.

Then, electrolysis was performed under the electrolytic conditions (Table 3) similar to Example 1 except that the temperature of the molten salt bath was kept at 430° C., resulting in a deposit including tungsten on the surface of the nickel plate.

Thereafter, the deposition state, composition, surface roughness, density, and relative density of the deposit were evaluated in a method similar to Example 1. The result is shown in Table 3.

As shown in Table 3, the deposit obtained using the molten salt bath of Example 2 was in the film-like deposition state, and had a large amount of tungsten with high purity, with a small surface roughness, high density, high relative density and high denseness.

Example 3

ZnCl₂, NaCl, KCl, and KF powders were each dried in a vacuum oven at 200° C. for 12 hours. WCl₄ powder was dried in a vacuum oven at 100° C. for 12 hours. Then, a mixture was prepared in a mol ratio of ZnCl₂, NaCl and KCl of 85:10:5. After KF and WCl₄ powders were each weighed in the above-noted glove box such that there were 4 mol of KF and 0.54 mol of WCl₄ for 100 mol of this mixture, these powders were put into the above-noted alumina crucible. The composition (mol ratio) of the raw materials put in the alumina crucible is shown in Table 1.

Thereafter, the alumina crucible was heated to allow the powders in the alumina crucible to be melted, similarly to Example 1. Thus, a molten salt bath of Example 3 was prepared. The composition (atomic %) of this molten salt bath is shown in Table 2.

Then, electrolysis was performed using the molten salt bath of Example 3 under the electrolytic conditions (Table 3) similar to Example 1 except that the temperature of the molten salt bath was kept at 380° C., resulting in a deposit including tungsten on the surface of the nickel plate.

Thereafter, the deposition state, composition, surface roughness, density, and relative density of the deposit were evaluated in a method similar to Example 1. The result is shown in Table 3.

As shown in Table 3, the deposit obtained using the molten salt bath of Example 3 was in the film-like deposition state, and had a large amount of tungsten with high purity, with a small surface roughness, high density, high relative density and high denseness.

Example 4

ZnCl₂, NaCl, CsCl (cesium chloride), and KF powders were each dried in a vacuum oven at 200° C. for 12 hours. WCl₄ powder was dried in a vacuum oven at 100° C. for 12 hours. Then, a mixture in a mol ratio of ZnCl₂, NaCl, and CsCl of 60:20:20 was put into the alumina crucible. Then, KF and WCl₄ were put into the aforementioned alumina crucible at 4 mol of KF and 0.54 mol of WCl₄ for 100 mol of the mixture. The composition (mol ratio) of the raw materials put in the alumina crucible is shown in Table 1.

Thereafter, the alumina crucible was heated to allow the powders in the alumina crucible to be melted, similarly to Example 1. Thus, a molten salt bath of Example 4 was prepared. The composition (atomic %) of this molten salt bath is shown in Table 2.

Then, electrolysis was performed using the molten salt bath of Example 4 under the electrolytic conditions (Table 3) similar to Example 1, resulting in a deposit including tungsten on the surface of the nickel plate.

Thereafter, the deposition state, composition, surface roughness, density, and relative density of the deposit were evaluated in a method similar to Example 1. The result is shown in Table 3.

As shown in Table 3, the deposit obtained using the molten salt bath of Example 4 was in the film-like deposition state, and had a large amount of tungsten with high purity, with a small surface roughness, high density, high relative density and high denseness.

Example 5

ZnCl₂, NaCl, KCl, KF, and WO₃ (tungstic trioxide) powders were each dried in a vacuum oven at 200° C. for 12 hours. WCl₄ powder was dried in a vacuum oven at 100° C. for 12 hours. After the ZnCl₂, NaCl, and KCl powders were each weighed in the above-noted glove box under Ar atmosphere in a mol ratio of 60:20:20, these powders were put into the above-noted alumina crucible in the same glove box.

In addition, after the KF, WCl₄ and WO₃ powders were each weighed in the aforementioned glove box such that there were 4 mol of KF, 0.27 mol of WCl₄, and 0.27 mol of WO₃ for 100 mol of the ZnCl₂, NaCl and KCl mixture put in the aforementioned alumina crucible, these powders were put into the aforementioned alumina crucible. The composition (mol ratio) of the raw materials put in the alumina crucible is shown in Table 1.

Then, the alumina crucible that contained ZnCl₂, NaCl, KCl, KF, WCl₄ and WO₃ was heated in the above-noted glove box to allow the powders in the alumina crucible to be melted. Thus, 500 g of a molten salt bath of Example 5 was prepared. The composition (atomic %) of this molten salt bath is shown in Table 2.

Then, electrolysis was performed using the molten salt bath of Example 5 under the electrolytic conditions (Table 3) similar to Example 1, resulting in a deposit including tungsten on the surface of the nickel plate.

Thereafter, the deposition state, composition, surface roughness, density, and relative density of the deposit were evaluated in a method similar to Example 1. The result is shown in Table 3.

As shown in Table 3, the deposit obtained using the molten salt bath of Example 5 was in the film-like deposition state, and had a large amount of tungsten with high purity, with a small surface roughness, high density, high relative density and high denseness.

Example 6

ZnBr₂ (zinc bromide), NaBr (sodium bromide), KBr (potassium bromide), and KF powders were each dried in a vacuum oven at 200° C. for 12 hours. WCl₄ powder was dried in a vacuum oven at 100° C. for 12 hours. After the ZnBr₂, NaBr, and KBr powders were each weighed in the above-noted glove box under Ar atmosphere in a mol ratio of 60:20:20, these powders were put into an alumina crucible in the same glove box.

In addition, after the KF and WCl₄ powders were each weighed in the aforementioned glove box such that there were 4 mol of KF and 0.5 mol of WCl₄ for 100 mol of the ZnBr₂, NaBr, and KBr mixture put in the aforementioned alumina crucible, these powders were put into the aforementioned alumina crucible. The composition (mol ratio) of the raw materials put in the alumina crucible is shown in Table 1.

Then, the alumina crucible that contained ZnBr₂, NaBr, KBr, KF, and WCl₄ was heated in the above-noted glove box to allow the powders in the alumina crucible to be melted. Thus, 500 g of the molten salt bath of Example 6 was prepared. The composition (atomic %) of this molten salt bath is shown in Table 2.

Then, electrolysis was performed using the molten salt bath of Example 6 under the electrolytic conditions (Table 3) similar to Example 1, resulting in a deposit including tungsten on the surface of the nickel plate.

Thereafter, the deposition state, composition, surface roughness, density, and relative density of the deposit were evaluated in a method similar to Example 1. The result is shown in Table 3.

As shown in Table 3, the deposit obtained using the molten salt bath of Example 6 was in the film-like deposition state, and had a large amount of tungsten with high purity, with a small surface roughness, high density, high relative density and high denseness.

Example 7

ZnCl₂, NaCl, KCl, and KF powders were each dried in a vacuum oven at 200° C. for 12 hours. WCl₄ powder was dried in a vacuum oven at 100° C. for 12 hours. A mixture of ZnCl₂, NaCl and KCl was prepared in a mol ratio of 49:30:21. After the KF and WCl₄ powders were each weighed in the aforementioned glove box such that there were 4 mol of KF and 0.54 mol of WCl₄ for 100 mol of this mixture, these powders were put into the aforementioned alumina crucible. The composition (mol ratio) of the raw materials put in the alumina crucible is shown in Table 1.

Thereafter, similarly to Example 1, the alumina crucible was heated to allow the powders in the alumina crucible to be melted, whereby a molten salt bath of Example 7 was prepared. The composition (atomic %) of this molten salt bath is shown in Table 2.

Then, electrolysis was performed using the molten salt bath of Example 7 under the electrolytic conditions (Table 3) similar to Example 1, resulting in a deposit including tungsten on the surface of the nickel plate.

Thereafter, the deposition state, composition, surface roughness, density, and relative density of the deposit were evaluated in a method similar to Example 1. The result is shown in Table 3.

As shown in Table 3, the deposit obtained using the molten salt bath of Example 7 was in the film-like deposition state, and had a large amount of tungsten with high purity, with a small surface roughness, high density, high relative density and high denseness.

Example 8

ZnCl₂, NaCl, KCl, and KF powders were each dried in a vacuum oven at 200° C. for 12 hours. WCl₄ powder was dried in a vacuum oven at 100° C. for 12 hours. A mixture of ZnCl₂, NaCl and KCl was prepared in a mol ratio of 70:15:15. After the KF and WCl₄ powders were each weighed in the aforementioned glove box such that there were 4 mol of KF and 0.54 mol of WCl₄ for 100 mol of this mixture, these powders were put into the aforementioned alumina crucible. The composition (mol ratio) of the raw materials put in the alumina crucible is shown in Table 1.

Thereafter, similarly to Example 1, the alumina crucible was heated to allow the powders in the alumina crucible to be melted, whereby a molten salt bath of Example 8 was prepared. The composition (atomic %) of this molten salt bath is shown in Table 2.

Then, electrolysis was performed using the molten salt bath of Example 8 under the electrolytic conditions (Table 3) similar to Example 1, resulting in a deposit including tungsten on the surface of the nickel plate.

Thereafter, the deposition state, composition, surface roughness, density, and relative density of the deposit were evaluated in a method similar to Example 1. The result is shown in Table 3.

As shown in Table 3, the deposit obtained using the molten salt bath of Example 8 was in the film-like deposition state, and had a large amount of tungsten with high purity, with a small surface roughness, high density, high relative density and high denseness.

Example 9

A deposit including tungsten on the surface of the nickel plate was obtained similarly to Example 1 except that the processes from weighing the powders to obtaining a deposit including tungsten were performed in the air. In Example 9, the composition (mol ratio) of the raw materials put in the alumina crucible is shown in Table 1 and the composition (atomic %) of the molten salt bath is shown in Table 2. Here, the oxygen content (atomic %) in the molten salt bath was calculated using the inert gas fusion infrared absorption method for a sample prepared by extracting a part of the molten salt bath. It is noted that the inclusion of oxygen in the molten salt bath of Example 9 is thought to be caused by intrusion of oxygen in the air.

Thereafter, the deposition state, composition, surface roughness, density, and relative density of the deposit were evaluated in a method similar to Example 1. The result is shown in Table 3.

As shown in Table 3, the deposit obtained using the molten salt bath of Example 9 was in the film-like deposition state, and had a large amount of tungsten with high purity, with a small surface roughness, high density, high relative density and high denseness.

Example 10

All the processes from weighing the powders to melting the powders in the alumina crucible were performed in the air. Here, in Example 10, the composition (mol ratio) of the raw materials put in the alumina crucible is shown in Table 1. Then, an alumina tube was inserted into the molten salt bath in the alumina crucible, and oxygen was introduced from the tube at a flow rate of 1 L/minute to perform bubbling with oxygen for one hour or longer. The composition (atomic %) of the resulting molten salt bath of Example 10 is shown in Table 2. Here, the oxygen content (atomic %) in the molten salt bath was calculated using the inert gas fusion infrared absorption method for a sample prepared by extracting a part of the molten salt bath. It is noted that the inclusion of oxygen in the molten salt bath of Example 10 is thought to be caused by intrusion of oxygen in the air and dissolution of oxygen introduced from the alumina tube.

Thereafter, electrolysis was performed under the electrolytic conditions (Table 3) similar to Example 1, resulting in a deposit including tungsten on the surface of the nickel plate.

Thereafter, the deposition state, composition, surface roughness, density, and relative density of the deposit were evaluated in a method similar to Example 1. The result is shown in Table 3.

As shown in Table 3, the deposit obtained using the molten salt bath of Example 10 was in the film-like deposition state, and had a large amount of tungsten with high purity, with a small surface roughness, high density, high relative density and high denseness.

Comparative Example 1

ZnCl₂ and NaCl powders were each dried in a vacuum oven at 200° C. for 12 hours. WCl₄ powder was dried in a vacuum oven at 100° C. for 12 hours. After the ZnCl₂ and NaCl powders were each weighed in the aforementioned glove box under Ar atmosphere in a mol ratio of 60:40, these powders were put into the aforementioned alumina crucible in the same glove box.

In addition, the WCl₄ powder was weighed in the aforementioned glove box such that there was 0.54 mol of WCl₄ for 100 mol of the ZnCl₂ and NaCl mixture put in the aforementioned alumina crucible. Thereafter, the WCl₄ powder was put into the aforementioned alumina crucible. The composition (mol ratio) of the raw materials put in the alumina crucible is shown in Table 1.

Then, the alumina crucible that contained ZnCl₂, NaCl and WCl₄ was heated in the aforementioned glove box to allow the powders to be melted. Thus, 500 g of a molten salt bath of Comparative Example 1 was prepared. The composition (atomic %) of this molten salt bath is shown in Table 2.

Then, electrolysis was performed using the molten salt bath of Comparative Example 1 under the electrolytic conditions (Table 3) similar to Example 1 except that the temperature of this molten salt bath was set at 400° C. Thus, a deposit including tungsten on the surface of the nickel plate was obtained.

Thereafter, the deposition state, composition, surface roughness, density, and relative density of the deposit were evaluated in a method similar to Example 1. The result is shown in Table 3.

As shown in Table 3, the deposit obtained using the molten salt bath of Comparative Example 1 was in the grain-like deposition state, and had an extremely small amount of tungsten, with a large surface roughness, with low denseness, density and relative density, as compared with the deposits of Examples 1-10.

Comparative Example 2

ZnCl₂, NaCl and KCl powders were each dried in a vacuum oven at 200° C. for 12 hours. WCl₄ powder was dried in a vacuum oven at 100° C. for 12 hours. After the ZnCl₂, NaCl and KCl powders were each weighed in the glove box under Ar atmosphere in a mol ratio of 60:20:20, these powders were put into the alumina crucible in the same glove box.

In addition, WCl₄ powder was weighed in the aforementioned glove box such that there was 0.54 mol of WCl₄ for 100 mol of the ZnCl₂, NaCl and KCl mixture put in the aforementioned alumina crucible. Thereafter, the WCl₄ powder was put into the aforementioned alumina crucible. The composition (mol ratio) of the raw materials put in the alumina crucible is shown in Table 1.

Then, the alumina crucible that contained ZnCl₂, NaCl, KCl and WCl₄ was heated in the aforementioned glove box to allow the powders to be melted. Thus, 500 g of a molten salt bath of Comparative Example 2 was prepared. The composition (atomic %) of this molten salt bath is shown in Table 2.

Then, electrolysis was performed using the molten salt bath of Comparative Example 2 under the electrolytic conditions (Table 3) similar to Example 1. Thus, a deposit including tungsten on the surface of the nickel plate was obtained.

Thereafter, the deposition state, composition, surface roughness, density, and relative density of the deposit were evaluated in a method similar to Example 1. The result is shown in Table 3.

As shown in Table 3, the deposit obtained using the molten salt bath of Comparative Example 2 was cracked, and had an extremely small amount of tungsten, with a large surface roughness, with low denseness, density and relative density as compared with the deposits of Examples 1-10.

TABLE 1 Composition (mol ratio) of Raw Materials ZnCl₂ NaCl KCl LiCl CsCl ZnBr₂ NaBr KBr KF WCl₄ WO₃ Example 1 60 20 20 0 0 0 0 0 4 0.54 0 Example 2 35 30 30 5 0 0 0 0 4 0.54 0 Example 3 85 10 5 0 0 0 0 0 4 0.54 0 Example 4 60 20 0 0 20 0 0 0 4 0.54 0 Example 5 60 20 20 0 0 0 0 0 4 0.27 0.27 Example 6 0 0 0 0 0 60 20 20 4 0.50 0 Example 7 49 30 21 0 0 0 0 0 4 0.54 0 Example 8 70 15 15 0 0 0 0 0 4 0.54 0 Example 9 60 20 20 0 0 0 0 0 4 0.54 0 Example 10 60 20 20 0 0 0 0 0 4 0.54 0 Comparative 60 40 0 0 0 0 0 0 0 0.54 0 Example 1 Comparative 60 20 20 0 0 0 0 0 0 0.54 0 Example 2

TABLE 2 Composition (atomic %) of Molten Salt Bath Zn Na K Li Cs Cl Br W F O Example 1 22.16 7.39 8.87 0 0 59.90 0 0.20 1.48 0 Example 2 14.25 12.21 13.84 2.03 0 55.82 0 0.22 1.63 0 Example 3 28.75 3.38 3.04 0 0 63.30 0 0.18 1.35 0 Example 4 22.16 7.39 1.48 0 7.39 59.90 0 0.20 1.48 0 Example 5 22.19 7.40 8.87 0 0 59.56 0 0.20 1.48 0.30 Example 6 22.18 7.39 8.87 0 0 0.74 59.15 0.19 1.48 0 Example 7 18.83 11.53 9.61 0 0 58.28 0 0.21 1.54 0 Example 8 24.94 5.34 6.77 0 0 61.33 0 0.19 1.43 0 Example 9 22.14 7.38 8.86 0 0 59.84 0 0.20 1.48 0.10 Example 10 22.10 7.37 8.84 0 0 59.72 0 0.20 1.47 0.30 Comparative 22.84 15.22 0 0 0 61.73 0 0.21 0 0 Example 1 Comparative 22.84 7.61 7.61 0 0 61.73 0 0.21 0 0 Example 2

TABLE 3 electrolytic conditions deposit current composition surface relative temperature density time deposition (atomic %) roughness density density (° C.) (mA/cm²) (hour) state W Zn O others (μm) (g/cm³) (%) Example 1 250 3 10 film 95 0 3 2 0.8 17.9 92.7 Example 2 430 3 10 film 93 1 4 2 1.2 17.3 89.6 Example 3 380 3 10 film 91 1 5 3 2.3 17.5 90.7 Example 4 250 3 10 film 94 0 4 2 0.7 17.7 91.7 Example 5 250 3 10 film 98 0 1 1 0.2 18.8 97.4 Example 6 250 3 10 film 93 1 3 3 1.1 17.5 90.7 Example 7 250 3 10 film 93 1 4 2 1.1 17.5 90.7 Example 8 250 3 10 film 92 1 4 3 1.3 17.4 90.2 Example 9 250 3 10 film 97 0 1 2 0.9 17.6 91.2 Example 10 250 3 10 film 98 0 1 1 0.7 17.5 90.7 Comparative 400 3 10 grain 50 2 12 36 18.6 14.2 73.6 Example 1 Comparative 250 3 10 cracking 20 35 10 35 29.3 9.8 50.8 Example 2

As can be seen from Table 2 and Table 3, when the molten salt bath including fluorine of Examples 1-10 was used, such deposits could be obtained that had a high purity of tungsten, had high density, high relative density and high denseness, and had a smooth surface, as compared with using the molten salt bath of Comparative Examples 1-2 not including fluorine.

Furthermore, as can be seen from Table 2 and Table 3, when the molten salt bath of Example 1 and Examples 4-10 was used that had a zinc content of 17 atomic % or more and 25 atomic % or less with respect to the entire molten salt bath, the deposits could be obtained at a lower temperature of the molten salt bath such as 250° C., as compared with using the molten salt bath of Examples 2-3.

Example 11

ZnCl₂, NaCl, KCl, and KF powders were each dried in a vacuum oven at 200° C. for 12 hours. Then, after the ZnCl₂, NaCl and KCl powders were each weighed in the aforementioned glove box under Ar atmosphere in a mol ratio of 60:20:20, these powders were put into the aforementioned alumina crucible in the same glove box.

In addition, KF and MoCl₃ (molybdenum trichloride) powders were each weighed in the aforementioned glove box such that there were 4 mol of KF and 0.54 mol of MoCl₃ for 100 mol of the ZnCl₂, NaCl and KCl mixture put in the aforementioned alumina crucible. Thereafter, these powders were put into the aforementioned alumina crucible. The composition (mol ratio) of the raw materials put in the alumina crucible is shown in Table 4.

Then, the alumina crucible that contained ZnCl₂, NaCl, KCl, KF and MoCl₃ was heated in the aforementioned glove box to allow the powders in the alumina crucible to be melted. Thus, 500 g of a molten salt bath of Example 11 was prepared. The composition (atomic %) of this molten salt bath is shown in Table 5.

Then, in the aforementioned glove box, a mirror-polished nickel plate having arithmetic mean roughness Ra of less than 10 nm as a cathode, a tungsten rod having a diameter of 5 mm as an anode, and a zinc rod having a diameter of 5 mm as a reference electrode were immersed in the molten salt bath of Example 11. Then, with the temperature of this molten salt bath kept at 250° C., electrolysis was performed under the electrolytic conditions (Table 6) with a potential between the cathode and the anode of 150 mV for three hours using a three electrode method in which the potential of the nickel plate serving as a cathode was controlled, resulting in a deposit including molybdenum on the surface of the nickel plate serving as a cathode.

Thereafter, the deposition state, composition, surface roughness, and density of the deposit were evaluated in a method similar to Example 1. Furthermore, the relative density (%) of the deposit was calculated by the following formula based on the density of the deposit as calculated above and the original density of molybdenum, where the original density of molybdenum, which is a metal intended to be deposited, is 10.22 (g/cm³).

The result is shown in Table 6.

the relative density (%) of the deposit=100×(the density of the deposit)/(the original density of molybdenum)

As shown in Table 6, the deposit (3 μm thick) obtained using the molten salt bath of Example 11 was in the film-like deposition state, and had a large amount of molybdenum with high purity, with a small-surface roughness, with high density, high relative density and high denseness.

Example 12

ZnCl₂, NaCl, KCl and KF powders were each dried in a vacuum oven at 200° C. for 12 hours. After the ZnCl₂, NaCl and KCl powders were each weighed in the aforementioned glove box under Ar atmosphere in a mol ratio of 60:20:20, these powders were put into the alumina crucible in the same glove box.

In addition, KF and MoCl₅ (molybdenum pentachloride) powders were each weighed in the aforementioned glove box such that there were 4 mol of KF and 0.54 mol of MoCl₅ for 100 mol of the ZnCl₂, NaCl and KCl mixture put in the aforementioned alumina crucible. Thereafter, these powders were put into the aforementioned alumina crucible. The composition (mol ratio) of the raw materials put in the alumina crucible is shown in Table 4.

Then, the alumina crucible that contained ZnCl₂, NaCl, KCl, KF and MoCl₅ was heated in the aforementioned glove box to allow the powders in the alumina crucible to be melted. Thus, 500 g of a molten salt bath of Example 12 was prepared. The composition (atomic %) of this molten salt bath is shown in Table 5.

Then, in the aforementioned glove box, a mirror-polished nickel plate having arithmetic mean roughness Ra of less than 10 nm as a cathode, a tungsten rod having a diameter of 5 mm as an anode, and a zinc rod having a diameter of 5 mm as a reference electrode were immersed in the molten salt bath of Example 12. Then, with the temperature of this molten salt bath kept at 250° C., electrolysis was performed under the electrolytic conditions (Table 6) with a potential between the cathode and the anode of 150 mV for three hours using a three electrode method in which the potential of the nickel plate serving as a cathode was controlled, resulting in a deposit including molybdenum on the surface of the nickel plate serving as a cathode.

Thereafter, the deposition state, composition, surface roughness, density, and relative density of the deposit were evaluated in a method similar to Example 11. The result is shown in Table 6.

As shown in Table 6, the deposit (0.5 μm thick) obtained using the molten salt bath of Example 12 was in the film-like deposition state, and had a large amount of molybdenum with high purity, with a small surface roughness, with high density, high relative density and high denseness.

Example 13

ZnCl₂, NaCl, KCl and KF powders were each dried in a vacuum oven at 200° C. for 12 hours. In addition, WO₃ powder was dried in a vacuum oven at 100° C. for 12 hours. After the ZnCl₂, NaCl and KCl powders were each weighed in the glove box under Ar atmosphere in a mol ratio of 60:20:20, these powders were put into the alumina crucible in the same glove box. in addition, KF and WO₃ powders were each weighed in the aforementioned glove box such that there were 4 mol of KF and 0.54 mol of WO₃ for 100 mol of the ZnCl₂, NaCl and KCl mixture put in the aforementioned alumina crucible. Thereafter, these powders were put into the aforementioned alumina crucible. The composition (mol ratio) of the raw materials put in the alumina crucible is shown in Table 4.

Then, the alumina crucible that contained ZnCl₂, NaCl, KCl, KF and WO₃ was heated in the aforementioned glove box to allow the powders in the alumina crucible to be melted. Thus, 500 g of a molten salt bath of Example 13 was prepared. The composition (atomic %) of this molten salt bath is shown in Table 5.

Then, in the aforementioned glove box, a mirror-polished nickel plate having arithmetic mean roughness Ra of less than 10 nm as a cathode, a tungsten rod having a diameter of 5 mm as an anode, and a zinc rod having a diameter of 5 mm as a reference electrode were immersed in the molten salt bath of Example 13. Then, with the temperature of this molten salt bath kept at 250° C., electrolysis was performed under the electrolytic conditions (Table 6) with a potential between the cathode and the anode of 60 mV for three hours using a three electrode method in which the potential of the nickel plate serving as a cathode was controlled, resulting in a deposit including tungsten on the surface of the nickel plate serving as a cathode.

Thereafter, the deposition state, composition, surface roughness, density, and relative density of the deposit were evaluated in a method similar to Example 1. The result is shown in Table 6.

As shown in Table 6, the deposit (0.5 μm thick) obtained using the molten salt bath of Example 13 was in the film-like deposition state, and had a large amount of tungsten with high purity, with a small surface roughness, with high density, high relative density and high denseness.

Example 14

ZnCl₂, NaCl, KCl and KF powders were each dried in a vacuum oven at 200° C. for 12 hours. Then, after ZnCl₂, NaCl and KCl powders were each weighed in the aforementioned glove box under Ar atmosphere in a mol ratio of 60:20:20, these powders were put into the alumina crucible in the same glove box.

In addition, KF and Ta₂O₅ (ditantalum pentaoxide) powders were each weighed in the aforementioned glove box such that there were 4 mol of KF and 0.54 mol of Ta₂O₅ for 100 mol of the ZnCl₂, NaCl and KCl mixture put in the aforementioned alumina crucible. Thereafter, these powders were put into the aforementioned alumina crucible. The composition (mol ratio) of the raw materials put in the alumina crucible is shown in Table 4.

Then, the alumina crucible that contained ZnCl₂, NaCl, KCl, KF and Ta₂O₅ was heated in the aforementioned glove box to allow the powders in the alumina crucible to be melted. Thus, 500 g of a molten salt bath of Example 14 was prepared. The composition (atomic %) of this molten salt bath is shown in Table 5.

Then, in the aforementioned glove box, a mirror-polished nickel plate having arithmetic mean roughness Ra of less than 10 nm as a cathode, a tungsten rod having a diameter of 5 mm as an anode, and a zinc rod having a diameter of 5 mm as a reference electrode were immersed in the molten salt bath of Example 14. Then, with the temperature of this molten salt bath kept at 250° C., electrolysis was performed under the electrolytic conditions (Table 6) with a potential between the cathode and the anode of 60 mV for three hours using a three electrode method in which the potential of the nickel plate serving as a cathode was controlled, resulting in a deposit including tantalum on the surface of the nickel plate serving as a cathode.

Thereafter, the deposition state, composition, surface roughness, and density of the deposit were evaluated in a method similar to Example 1. Furthermore, the relative density (%) of the deposit was calculated by the following formula based on the density of the deposit as calculated above and the original density of tantalum, where the original density of tantalum, which is a metal intended to be deposited, is 16.65 (g/cm³).

The result is shown in Table 6.

the relative density (%) of the deposit=100×(the density of the deposit)/(the original density of tantalum)

As shown in Table 6, the deposit (0.5 μm thick) obtained using the molten salt bath of Example 14 was in the film-like deposition state, and had a large amount of tantalum with high purity, with a small surface roughness, with high density, high relative density and high denseness.

Example 15

ZnCl₂, NaCl, KCl and KF powders were each dried in a vacuum oven at 200° C. for 12 hours. Then, after the ZnCl₂, NaCl and KCl powders were each weighed in the aforementioned glove box under Ar atmosphere in a mol ratio of 60:20:20, these powders were put into the alumina crucible in the same glove box.

In addition, KF powder was weighed in the aforementioned glove box at 4 mol for 100 mol of the ZnCl₂, NaCl and KCl mixture put in the aforementioned alumina crucible. Then, the weighed KF powder was put into the aforementioned alumina crucible.

Then, the alumina crucible that contained ZnCl₂, NaCl, KCl, and KF was heated in the aforementioned glove box to allow the powders in the alumina crucible to be melted. Thereafter, TiCl₄ was weighed in the above-noted glove box at 0.54 mol for 100 mol of the ZnCl₂, NaCl and KCl mixture put in the aforementioned alumina crucible. The weighed TiCl₄ was added to the aforementioned alumina crucible. Thus, 500 g of a molten salt bath of Example 15 was prepared. The composition (mol ratio) of the raw materials used for preparing this molten salt bath is shown in Table 4 and the composition (atomic %) of this molten salt bath is shown in Table 5.

Then, in the aforementioned glove box, a mirror-polished nickel plate having arithmetic mean roughness Ra of less than 10 nm as a cathode, a tungsten rod having a diameter of 5 mm as an anode, and a zinc rod having a diameter of 5 mm as a reference electrode were immersed in the molten salt bath of Example 15. Then, with the temperature of this molten salt bath kept at 250° C., electrolysis was performed under the electrolytic conditions (Table 6) with a potential between the cathode and the anode of 60 mV for six hours using a three electrode method in which the potential of the nickel plate serving as a cathode was controlled, resulting in a deposit including titanium on the surface of the nickel plate serving as a cathode.

Thereafter, the deposition state, composition, surface roughness, and density of the deposit were evaluated in a method similar to Example 1. Furthermore, the relative density (%) of the deposit was calculated by the following formula based on the density of the deposit as calculated above and the original density of titanium, where the original density of titanium, which is a metal intended to be deposited, is 4.54 (g/cm³).

The result is shown in Table 6.

the relative density (%) of the deposit=100×(the density of the deposit)/(the original density of titanium)

As shown in Table 6, the deposit (0.1 μm thick) obtained using the molten salt bath of Example 15 was in the film-like deposition state, and had a large amount of titanium with high purity, with a small surface roughness, with high density, high relative density and high denseness.

Example 16

ZnCl₂, NaCl, KCl and KF powders were each dried in a vacuum oven at 200° C. for 12 hours. Then, after the ZnCl₂, NaCl and KCl powders were each weighed in the aforementioned glove box under Ar atmosphere in a mol ratio of 60:20:20, these powders were put into the alumina crucible in the same glove box.

In addition, KF powder was weighed in the aforementioned glove box at 4 mol for 100 mol of the ZnCl₂, NaCl and KCl mixture put in the aforementioned alumina crucible. Then, the weighed KF powder was put into the aforementioned alumina crucible.

Then, the alumina crucible that contained ZnCl₂, NaCl, KCl, and KF was heated in the aforementioned glove box to allow the powders in the alumina crucible to be melted. Thereafter, TiCl₄ was weighed in the above-noted glove box at 1.1 mol for 100 mol of the ZnCl₂, NaCl and KCl mixture put in the aforementioned alumina crucible. The weighed TiCl₄ was added to the aforementioned alumina crucible. Thus, 500 g of a molten salt bath of Example 16 was prepared. The composition (mol ratio) of the raw materials used for preparing this molten salt bath is shown in Table 4 and the composition (atomic %) of the molten salt bath is shown in Table 5.

Then, in the aforementioned glove box, a mirror-polished nickel plate having arithmetic mean roughness Ra of less than 10 nm as a cathode, a tungsten rod having a diameter of 5 mm as an anode, and a zinc rod having a diameter of 5 mm as a reference electrode were immersed in the molten salt bath of Example 16. Then, with the temperature of this molten salt bath kept at 250° C., electrolysis was performed under the electrolytic conditions (Table 6) with a potential between the cathode and the anode of 60 mV for three hours using a three electrode method in which the potential of the nickel plate serving as a cathode was controlled, resulting in a deposit including titanium on the surface of the nickel plate serving as a cathode.

Thereafter, the deposition state, composition, surface roughness, density, and relative density of the deposit were evaluated in a method similar to Example 15. The result is shown in Table 6.

As shown in Table 6, the deposit (0.1 μm thick) obtained using the molten salt bath of Example 16 was in the film-like deposition state, and had a large amount of titanium with high purity, and with a small surface roughness, with high density, high relative density and high denseness.

Example 17

ZnCl₂, NaCl, KCl and KF powders were each dried in a vacuum oven at 200° C. for 12 hours. After the ZnCl₂, NaCl and KCl powders were weighed in the glove box under Ar atmosphere in a mol ratio of 60:20:20, these powders were put into the alumina crucible in the same glove box.

In addition, KF powder was weighed in the aforementioned glove box at 4 mol for 100 mol of the ZnCl₂, NaCl and KCl mixture put in the aforementioned alumina crucible. Then, the weighed KF powder was put into the aforementioned alumina crucible.

Then, the alumina crucible that contained ZnCl₂, NaCl, KCl, and KF was heated in the aforementioned glove box to allow the powders in the alumina crucible to be melted. Thereafter, TiCl₄ was weighed in the above-noted glove box at 2.5 mol for 100 mol of the ZnCl₂, NaCl and KCl mixture put in the aforementioned alumina crucible. The weighed TiCl₄ was added to the aforementioned alumina crucible. Thus, 500 g of a molten salt bath of Example 17 was prepared. The composition (mol ratio) of the raw materials used for preparing this molten salt bath is shown in Table 4 and the composition (atomic %) of the molten salt bath is shown in Table 5.

Then, in the aforementioned glove box, a mirror-polished nickel plate having arithmetic mean roughness Ra of less than 10 nm as a cathode, a tungsten rod having a diameter of 5 mm as an anode, and a zinc rod having a diameter of 5 mm as a reference electrode were immersed in the molten salt bath of Example 17. Then, with the temperature of this molten salt bath kept at 250° C., electrolysis was performed under the electrolytic conditions (Table 6) with a potential between the cathode and the anode of 60 mV for eight hours using a three electrode method in which the potential of the nickel plate serving as a cathode was controlled, resulting in a deposit including titanium on the surface of the nickel plate serving as a cathode.

Thereafter, the deposition state, composition, surface roughness, density, and relative density of the deposit were evaluated in a method similar to Example 15. The result is shown in Table 6.

As shown in Table 6, the deposit (0.5 μm thick) obtained using the molten salt bath of Example 17 was in the film-like deposition state, and had a large amount of titanium with high purity, with a small surface roughness, with high density, high relative density and high denseness.

Example 18

ZnCl₂, NaCl, KCl and KF powders were each dried in a vacuum oven at 200° C. for 12 hours. Then, after the ZnCl₂, NaCl and KCl powders were each weighed in the glove box under Ar atmosphere in a mol ratio of 60:20:20, these powders were put into the alumina crucible in the same glove box.

In addition, KF and NbCl₅ (niobium pentachloride) powders were each weighed in the aforementioned glove box such that there were 4 mol of KF and 0.54 mol of NbCl₅ for 100 mol of the ZnCl₂, NaCl and KCl mixture put in the aforementioned alumina crucible. Thereafter, these powders were put into the aforementioned alumina crucible. The composition (mol ratio) of the raw materials put in the alumina crucible is shown in Table 4.

Then, the alumina crucible that contained ZnCl₂, NaCl, KCl, KF and NbCl₅ was heated in the aforementioned glove box to allow the powders in the alumina crucible to be melted. Thus, 500 g of a molten salt bath of Example 18 was prepared. The composition (atomic %) of this molten salt bath is shown in Table 5.

Then, in the aforementioned glove box, a mirror-polished nickel plate having arithmetic mean roughness Ra of less than 10 nm as a cathode, a tungsten rod having a diameter of 5 mm as an anode, and a zinc rod having a diameter of 5 mm as a reference electrode were immersed in the molten salt bath of Example 18. Then, with the temperature of this molten salt bath kept at 250° C., electrolysis was performed under the electrolytic conditions (Table 6) with a potential between the cathode and the anode of 60 mV for three hours using a three electrode method in which the potential of the nickel plate serving as a cathode was controlled, resulting in a deposit including niobium on the surface of the nickel plate serving as a cathode.

Thereafter, the deposition state, composition, surface roughness, and density of the deposit were evaluated in a method similar to Example 1. Furthermore, the relative density (%) of the deposit was calculated by the following formula based on the density of the deposit as calculated above and the original density of niobium, where the original density of niobium, which is a metal intended to be deposited, is 8.57 (g/cm³).

The result is shown in Table 6.

the relative density (%) of the deposit=100×(the density of the deposit)/(the original density of niobium)

As shown in Table 6, the deposit (0.5 μm thick) obtained using the molten salt bath of Example 18 was in the film-like deposition state, and had a large amount of niobium with high purity, with a small surface roughness, with high density, high relative density and high denseness.

Example 19

ZnCl₂, NaCl, KCl and KF powders were each dried in a vacuum oven at 200° C. for 12 hours. Then, after the ZnCl₂, NaCl and KCl powders were each weighed in the glove box under Ar atmosphere in a mol ratio of 60:20:20, these powders were put into the alumina crucible in the same glove box.

In addition, KF and VCl₂ (vanadium dichloride) powders were each weighed in the aforementioned glove box such that there were 4 mol of KF and 0.54 mol of VCl₂ for 100 mol of the ZnCl₂, NaCl and KCl mixture put in the aforementioned alumina crucible. Thereafter, these powders were put into the aforementioned alumina crucible. The composition (mol ratio) of the raw materials put in the alumina crucible is shown in Table 4.

Then, the alumina crucible that contained ZnCl₂, NaCl, KCl, KF and VCl₂ was heated in the aforementioned glove box to allow the powders in the alumina crucible to be melted. Thus, 500 g of a molten salt bath of Example 19 was prepared. The composition (atomic %) of this molten salt bath is shown in Table 5.

Then, in the aforementioned glove box, a mirror-polished nickel plate having arithmetic mean roughness Ra of less than 10 nm as a cathode, a tungsten rod having a diameter of 5 mm as an anode, and a zinc rod having a diameter of 5 mm as a reference electrode were immersed in the molten salt bath of Example 19. Then, with the temperature of this molten salt bath kept at 250° C., electrolysis was performed under the electrolytic conditions (Table 6) with a potential between the cathode and the anode of 60 mV for three hours using a three electrode method in which the potential of the nickel plate serving as a cathode was controlled, resulting in a deposit including vanadium on the surface of the nickel plate serving as a cathode.

Thereafter, the deposition state, composition, surface roughness, and density of the deposit were evaluated in a method similar to Example 1. Furthermore, the relative density (%) of the deposit was calculated by the following formula based on the density of the deposit as calculated above and the original density of vanadium, where the original density of vanadium, which is a metal intended to be deposited, is 6.11 (g/cm³). The result is shown in Table 6.

As shown in Table 6, the deposit (0.5 μm thick) obtained using the molten salt bath of Example 19 was in the film-like deposition state, and had a large amount of vanadium with high purity, with a small surface roughness, with high density, high relative density and high denseness.

TABLE 4 Composition (mol ratio) of Raw Materials ZnCl₂ NaCl KCl KF MoCl₃ MoCl₅ WO₃ Ta₂O₅ TiCl₄ NbCl₅ VCl₂ Example 11 60 20 20 4 0.54 0 0 0 0 0 0 Example 12 60 20 20 4 0 0.54 0 0 0 0 0 Example 13 60 20 20 4 0 0 0.54 0 0 0 0 Example 14 60 20 20 4 0 0 0 0.54 0 0 0 Example 15 60 20 20 4 0 0 0 0 0.54 0 0 Example 16 60 20 20 4 0 0 0 0 1.1 0 0 Example 17 60 20 20 8 0 0 0 0 2.5 0 0 Example 18 60 20 20 4 0 0 0 0 0 0.54 0 Example 19 60 20 20 4 0 0 0 0 0 0 0.54

TABLE 5 Composition (atomic %) of Molten Salt Bath Zn Na K Cl O F W Mo Ta Ti Nb V Example 11 22.21 7.40 8.88 59.82 0 1.48 0 0.20 0 0 0 0 Example 12 22.12 7.37 8.85 59.98 0 1.47 0 0.20 0 0 0 0 Example 13 22.21 7.40 8.88 59.22 0.60 1.48 0.20 0 0 0 0 0 Example 14 22.08 7.36 8.83 58.87 0.99 1.47 0 0 0.40 0 0 0 Example 15 22.16 7.39 8.87 59.90 0 1.48 0 0 0 0.20 0 0 Example 16 21.95 7.32 8.78 60.10 0 1.46 0 0 0 0.40 0 0 Example 17 20.80 6.93 9.71 58.93 0 2.77 0 0 0 0.87 0 0 Example 18 22.12 7.37 8.85 59.98 0 1.47 0 0 0 0 0.20 0 Example 19 22.25 7.42 8.90 59.74 0 1.48 0 0 0 0 0 0.20

TABLE 6 deposits electrolytic conditions surface relative temperature potential time deposition composition (atomic %) roughness density density (° C.) (mV) (hr) state W Mo Ta Ti Nb V Zn O others (μm) (g/cm³) (%) Example 11 250 150 3 film 0 99 0 0 0 0 0 0.5 0.5 2.6 9.8 95.9 Example 12 250 150 3 film 0 98 0 0 0 0 0 1.7 0.3 1.5 10.1 98.8 Example 13 250 60 3 film 99 0 0 0 0 0 0 0.7 0.3 0.1 18.8 97.4 Example 14 250 60 3 film 0 0 99.1 0 0 0 0 0.1 0.8 1.9 15.1 90.7 Example 15 250 60 6 film 0 0 0 99 0 0 0 0.2 0.8 0.8 4.1 90.3 Example 16 250 60 3 film 0 0 0 99.1 0 0 0 0.2 0.7 1.4 4.2 92.5 Example 17 250 60 8 film 0 0 0 98.9 0 0 0 0.3 0.8 2.3 4.1 90.3 Example 18 250 60 3 film 0 0 0 0 99.1 0 0 0.1 0.8 3.2 8.1 94.5 Example 19 250 60 3 film 0 0 0 0 0 98.2 0 0.5 1.3 2.6 5.8 94.9

Example 20

A titanium layer was formed by sputtering titanium at a thickness of 0.3 μm on a surface of a disk-like silicon substrate having a diameter of 3 inches. Then, a photoresist of a width of 1 cm×a length of 1 cm×a thickness of 30 μm, made of PMMA, was applied on the titanium layer. Then, SR light (synchrotron radiation) was applied to a part of the photoresist, and that part of the photoresist which was irradiated with SR light was selectively removed, whereby a stripe-like resist pattern was formed on the titanium layer with line/space of 50 μm/50 μm.

Then, using the above-noted silicon substrate having the resist pattern formed thereon as a cathode and a tungsten rod as an anode, these electrodes were immersed in 1000 g of molten salt bath having the same composition as the molten salt bath of Example 6 in the glove box under Ar atmosphere. Then, with the molten salt bath kept at 250° C., constant-current electrolysis was performed by feeding electric current of 3 mA per cm² of the titanium layer on the silicon substrate (current density 3 mA/cm²) across these electrodes for 60 hours, resulting in a deposit including tungsten on the titanium layer.

After completion of the constant-current electrolysis, the silicon substrate was taken out from the glove box. Then, the silicon substrate was washed with water in order to remove salt attached to the silicon substrate. Next, after the silicon substrate was dried, plasma ashing was performed using a mixture gas of CF₄ (carbon tetrafluoride) and O₂ (oxygen), whereby the photoresist on the titanium layer was removed. Finally, the deposit on the titanium layer was mechanically stripped, resulting in an electroformed product with high purity of tungsten, with high density and high denseness and having a smooth surface.

It should be understood that the embodiments and examples disclosed herein are not limitative but illustrative in all aspects. The scope of the present invention is shown not in the foregoing description but in the claims, and all changes within the meaning and range of equivalency of the claims are intended to be embraced therein.

INDUSTRIAL APPLICABILITY

The molten salt bath in accordance with the present invention contains at least one kind selected from the group consisting of chlorine, bromine and iodine, zinc, at least two kinds of alkali metals, and fluorine, so that the use of the molten salt bath of the present invention results in a deposit with high purity, high density and high denseness and having a smooth surface. 

1. A molten salt bath including at least one kind selected from the group consisting of chlorine, bromine and iodine, zinc, at least two kinds of alkali metals, and fluorine.
 2. The molten salt bath according to claim 1, characterized by including oxygen.
 3. The molten salt bath according to claim 1, characterized by including at least one kind selected from the group consisting of tungsten, chromium, molybdenum, tantalum, titanium, zirconium, vanadium, hafnium, and niobium.
 4. The molten salt bath according to claim 1, characterized by being made of at least two kinds selected from the group consisting of sodium, potassium and cesium as said alkali metals, at least one kind of chlorine and bromine, zinc, and fluorine.
 5. The molten salt bath according to claim 1, characterized in that a content of said zinc is at least 14 atomic % and at most 30 atomic % of said molten salt bath as a whole.
 6. The molten salt bath according to claim 1, characterized in that a content of said zinc is at least 17 atomic % and at most 25 atomic % of said molten salt bath as a whole.
 7. The molten salt bath according to claim 1, characterized in that a content of said fluorine is at least 0.1 atomic % and at most 20 atomic % of said molten salt bath as a whole.
 8. A deposit obtained using the molten salt bath according to claim
 1. 9. The deposit according to claim 8, characterized in that the deposit is formed in a state in which said molten salt bath includes at least 0.01 atomic % of oxygen.
 10. The deposit according to claim 8, characterized in that arithmetic mean roughness Ra (JIS B0601-1994) of a surface of said deposit is at most 3 μm.
 11. The deposit according to claim 8, characterized in that a relative density of said deposit is at least 85%.
 12. A method of manufacturing a metal product comprising the steps of: forming a resist pattern on a conductive substrate to expose a part of said conductive substrate; immersing the conductive substrate having said resist pattern formed thereon in the molten salt bath according to claim 1; and depositing a metal from said molten salt bath on the exposed part of said conductive substrate.
 13. The method of manufacturing a metal product according to claim 12, characterized in that a temperature of said molten salt bath is at most 250° C.
 14. A metal product manufactured using the method of manufacturing a metal product according to claim
 13. 